This invention relates to an air/fuel ratio control unit for an internal combustion engine, and more particularly to an improved method and apparatus for controlling the air/fuel ratio of an engine in response to parameters including altitude changes.
As should be readily apparent, it is extremely desirable to provide an accurate air/fuel ratio control for internal combustion engines not only to improve fuel economy but also to reduce unwanted exhaust gas emissions. Therefore, a wide variety of types of control strategies have been provided. Basically, the fuel/air ratio is controlled in response to engine speed and load as determined by throttle opening or another parameter. However, it also known that the desirable air/fuel ratio is dependent upon atmospheric pressure or altitude. Therefore, it has been the practice to provide altitude or atmospheric pressure compensation for the air/fuel ratio to further improve engine performance and fuel economy. However, the previously proposed systems have not been completely effective in providing such control.
The reason for this can be best understood by reference to FIG. 1 which is a family of curves showing engine power and fuel supply amount per revolution of the engine at various engine speeds. As may be seen, as the engine speed increases, the amount of fuel required to produce maximum power also increases. The curves N1, N2, N3, N4, and N5 show the curves at 5 progressively increasing engine speeds. The points Q1, Q2, Q3, Q4, and Q5 indicate the optimum fuel to be supplied to the engine to achieve maximum horsepower. However, most control strategies adopt a fuel control that increases the amount of fuel supplied to the engine above that required for maximum power at high speed, high load conditions. This is done to insure against over-heating.
When conventional systems make altitude compensation they follow fuel supply curves shown by the dotted line curves and the quantity of fuel supplied is varied generally proportionally to the increase in altitude so that as the altitude increases or atmospheric pressure decreases at low speeds the fuel supply is changed from Q1 to Q1a. At the higher engine speed N5 the fuel set at standard pressure is on the rich side and is picked as the amount Q5' rather than Q5. This is done for the aforenoted reason. Therefore, if the altitude increases, the fuel is decreased in the same proportion to the point Q5'a. It has been found that excess fuel is supplied. The reason for this is that the engine temperature tends to decrease as the altitude increases with all other factors constant. Therefore, it is not necessary to provide the additional enrichment to avoid over-heating when the altitude increases.
It is, therefore, a principal object of this invention to provide an improved method and apparatus for controlling the air/fuel ratio for an internal combustion engine and making appropriate altitude compensation therein.
It is a further object of this invention to provide an engine fuel supply control that will insure against over-heating under a high speed high load conditions but which will not be overly rich when the altitude increases or atmospheric pressure decreases.
It is a further object of this invention to provide an improved fuel/air supply and control wherein in addition to altitude compensation other factors such as engine speed and/or load are also reflected in the altitude compensation.